Electric power is delivered as direct current (DC) or as alternating current (AC). Direct current involves transferring electric power in the form of an electron current flow which consists of electrons migrating through a conductor under the influence of an electromotive force known as voltage potential. In contrast, alternating current transfers electric power in the form of a space-time distortion known as a Transversal Electro-Magnetic Wave which is located and travels within the area between the conductors.
Alternating current preferably is used over direct current for sending electric power through an electrically conductive wire or cable system. This is because the flow characteristics of the alternating current may be transformed by a transformer to optimize the use (and losses) in the conductor(s) in the electrically conductive wire or cable system. As a result, the standard power distribution system in the United States involves using alternating current which operates at a frequency of 60 cycles per second(Hertz). Power transformers located on the ground and on poles convert the relatively high voltage power of the alternating current transmitted through the cross-country lines (upwards of 500,000 volts) to a more practical 120 volts such as, for example, would be used in the home.
As the alternating current frequency of electric power is raised, the size of the transformer becomes smaller. For example, the electrical power in aircraft is run at 400 Hertz and not at 60 Hertz as in the home. This higher frequency means that the transformers are smaller and lighter and, therefore, more suitable for transport on aircraft. In addition, as the frequency of the electrical power increases, the physical construction of the power cable must change. Specifically, high frequency electrical energy is served best by a coaxial cable construction as the electrical power wave may be completely contained within the cable structure. Furthermore, coaxial cables ensure that energy does not leak out of the cables and become wasted radiated electromagnetic power.
Thus, not only is power transfer more efficient with coaxial cables, but they do not contaminate the local environment with electrical or radio noise. Coaxial cables are also inherently round and symmetrical about their central axes which enables them to pull into job sites easily and fit through grommets and fittings without problems. Coaxial cables generally do not include fillers or artificial shaping material. Thus, coaxial cables are presently used to transmit power or data in the electric domain. Specifically, metal, i.e., copper coaxial cables are used to transmit electric power or data (analog or digital). In contrast, fiber optic cables are used to transmit high speed fiber optic data. Both types of cables are often simultaneously needed for a specific use. Thus, efforts have been made to combine a mixture of individual metal cables and fiber optic cables within a single cable construction. This involves positioning a mixture of individual copper and fiber optic cables into one jacket. This type of construction is shown on page 210 of the 1992 Belden Master Catalog.
While the above-described cable includes both individual metal and fiber optic cables that are combined into a single cable construction, there are problems associated with its use. First, the cable jacket generally is not effective for retaining the symmetrical and round shape of the cable. Such a lack of symmetry in the shape of the cable interferes with cable usage.
As previously mentioned, a symmetrical and round cable construction is essential to effective usage of the cable. Thus, a cable without such a construction does not permit the cable to be used in some instances.
Second, packaging a mixture of individual metal insulated conductors and fiber optic cables into a single cable construction is both time-consuming and costly.